Apparently, I haven't been active for months after all, but yes, someone else must be sitting with quite a pile of cobble. Or related things.
* Bla suspiciously glances at vh's 30k stone!
There was a rush of taking cobblestone from spawntown before it ran out. I think almost everyone did it to some extent, I took 3 small chests worth to use on roads back in early December, all of the excess cobble that I had from then has since been taken from my public storage.